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# Can an object be accelerating and yet -not- moving?

MattDavis

1
Wed 13 Feb, 2013 08:55 am
@engineer,
Yep.
I agree.
0 Replies

dalehileman

1
Wed 13 Feb, 2013 01:50 pm
@becquerel,
Quote:
I don't think so - the question is from the point of view of an (I assume) stationary observer who is observing an object that is actually accelerating. ……..
Bec Tho I'm no physicist of course, I've long been intrigued by the notion of relativity as applied to the yet-to-be-discovered "gravity wave"

Of course there's supposedly no such thing as a "stationary" object. I speculate you sitting there in your rocket ship out in space somewhere as a big planetoid hurtles by; so owing to its moving field in order to keep still you find it necessary to fire up your rockets. But Andy, who dwells on the massive body, considers himself at rest; so to him you're accelerating

Quote:
…... "You see an object that is not moving. At that moment…….here, "the object may or may not be accelerating" is also a correct answer. The explanation is, "the object may be accelerating, just momentarily at rest……...don't really understand how an object could be accelerating and yet…..at rest…..
Dunno. Maybe the object is reversing direction

Edited to note that might be what Rog and Eng are suggesting above. It's apparent those other guys are 'way beyond me

Quote:
You're welcome Bec but not sure I've been of much help, I'm a rank amateur at this stuff
maxdancona

1
Wed 13 Feb, 2013 02:01 pm
@dalehileman,
Quote:
Of course there's supposedly no such thing as a "stationary" object.

That is incorrect. In physics, any object with a velocity of zero is stationary by definition.

Of course, you need to specify the frame of reference to measure velocity, but once you have done that any object that isn't moving in that frame of reference is stationary.
dalehileman

1
Wed 13 Feb, 2013 02:11 pm
@maxdancona,
Quote:
…...but once you have done that any object that isn't moving in that frame of reference is stationary.
Yea Max I understand how that works. However my speculation entails one ref frame moving with respect to another and possible interactions

Again, however, I'll concede as a rank amateur that the "gravity wave" I envision hasn't yet been confirmed, I could be totally off course (no pun)

But incidentally this brings up another subject that I've long wondered about, which might even merit a new thread, and that's the notion of the Universe Herself being such a frame, where an object could be said absolutely still
contrex

1
Wed 13 Feb, 2013 02:46 pm
@engineer,
engineer wrote:
At that moment, the velocity is zero but it is still accelerating.

Yes, because an accelerating object is an object that is changing its velocity.
dalehileman

0
Wed 13 Feb, 2013 05:23 pm
@contrex,
Quote:
Yes, because an accelerating object is an object that is changing its velocity.
Intuition says yes the reversing object is accelerating although the idea of an infinitesimal period of stoppage is troublesome, a moment of zero duration

Maybe we're getting into philosophy
maxdancona

2
Wed 13 Feb, 2013 08:56 pm
@dalehileman,
Why is it troublesome? This is math, not philosophy.

0 is just a number. Does it trouble you that at some point the object thrown upward is traveling at a speed of 2 m/s (for the same "zero duration") and soon after at a speed of 1.8 m/s?

A ball thrown upward at 29.4 m/s (a number I chose to make the calculation easy but any number will work). Every second it will be going 9.8 m/s slower (i.e. we subtract 9.8 m/s from its speed).

After 1 second it will be going 19.6 m/s upward (I just subtracted 9.8 m/s from the original speed.

After 2 seconds it will be going 9.8 m/s upward (again I just subtracted another 9.8 m/s)

After 3 seconds it will be going 0 m/s (Yes 0 m/s means stopped)

After 4 seconds it will be going -9.8 m/s upward which is the same as 9.8 m/s downward (again I simply subtracted 9.8m/s).

After 5 seconds it will be going 19.6 m/s downward.

There is nothing complicated or mystical about this. This has nothing to do with relativity or anything you couldn't understand with what you learned in a standard high school science class.

It is simply the definition of acceleration. An acceleration of -9.8 m/s/s means that every second you subtract 9.8 m/s from the speed.

As you see from the example above, 0m/s is quite easy to hit. It shouldn't surprise you. After all 0 is just a number and a speed of 0 m/s is no more surprising than any other speed (like 2 m/s, or 100 m/s).

maxdancona

2
Wed 13 Feb, 2013 08:58 pm
@dalehileman,
I am not talking about General Relativity here. I am talking about classical high school Physics (which anyone should master before attempting to understand General Relativity).

Galileo understood that motion had to be measured based on a frame of reference hundreds of years before Einstein figured out Relativity. This has nothing to do with gravity waves.
0 Replies

dalehileman

0
Thu 14 Feb, 2013 12:44 pm
@maxdancona,
Quote:
0 is just a number. Does it trouble you that at some point…...a speed of 2 m/s (for the same "zero duration")…….?
Yes Max it does; somehow zero seems to have a special significance, don't ask me why, it's Intuition, don't be angry
maxdancona

1
Thu 14 Feb, 2013 12:45 pm
@dalehileman,
Intuition is the enemy of logic and reason.
dalehileman

0
Thu 14 Feb, 2013 12:48 pm
@maxdancona,
Quote:
a speed of 0 m/s is no more surprising than any other speed
To the contrary; without it we'd still be living in caves and hitting each other over the head

…whereas today we do only the latter

…….but it's generally acknowledged Einstein depended largely on Intuition developing his Theory of Relativity
maxdancona

1
Thu 14 Feb, 2013 01:16 pm
@dalehileman,
Quote:
…….but it's generally acknowledged Einstein depended largely on Intuition developing his Theory of Relativity

Quite the contrary!

Read Einstein's seminal paper on Relativity here (I link to the English translation of the original work in German).

http://www.fourmilab.ch/etexts/einstein/specrel/www/

Einstein's Theory of Relativity relies solely on Mathematics and Reason. It is genius because it is counter-intuitive. The idea that time is relative is not something that anyone's intuition told them (for thousands of years of thought on the subject).

It was logic that led to this theory.

Intuition can't be trusted and is quite often wrong. If intuition was valuable to find the truth, then we wouldn't need the arduous process of scientific experimentation and discovery.
georgeob1

1
Thu 14 Feb, 2013 01:18 pm
@raprap,
raprap wrote:

Its a boundary condition. Acceleration is the second deritive of displacement. Velocity is the first deritive.

If you are to solve a differential for displacement or velocity of a mass that is accelerated, you must have a boundary condition.

In this case this boundary a mass is being accelerated and at zero time the velocity is zero.

V=ds/dt
a=dV/dt=d^2s/dt^2
@t=0 V=0

Rap

The boundary condition is needed only to find the particular solution for the situation. In general integrating the equation yields the solution;

s = Const #1 * t + 1/2 a* t ^2 + Const #2

where Const #1 & Const #2 are the constants of integration, equalling the initial velocity and the initial position respectively.

There is no violation of the fundamental theorem of calculus. Engineer was entirely correct inhis first post.
0 Replies

dalehileman

0
Thu 14 Feb, 2013 01:42 pm
@maxdancona,
Quote:
Einstein's Theory of Relativity relies solely on Mathematics and Reason.
….promoted by Intuition

Quote:
It is genius because it is counter-intuitive.
That doesn't mean Intuition wasn't involved in its development

Quote:
The idea that time is relative is not something that anyone's intuition told them…..
Yes I agree it's puzzling intuitionally as is increasing mass, contrction, and the like

Perhaps we could discuss this in another thread where not OT
maxdancona

1
Thu 14 Feb, 2013 02:02 pm
@dalehileman,
The original question has be resolved, so why not discuss intuition here. It is a related topic-- since in this case is an example where the answer from "intuition" is mathematically wrong.

I am an engineer, and I play poker. Both of these pursuits are highly mathematical. I intentionally exclude intuition from my decision making.

Intuition is valuable in one rare case; when you don't have time for logic or reason. The only advantage of intuition is that it is fast. It let's you make a decision, right or wrong, quickly, and intuition is correct some of the time just by random.

I do use imagination (which is very different from intuition). Imagination is about possibilities. Intuition is about conclusions. Imagination opens your mind to explore new possibilities. Intuition closes your mind by making a decision before you have consciously thought it out. Einstein spoke about the importance of imagination. He was against things like "common sense" which he referred to as "a collection of prejudices acquired before age eighteen".

For important decisions where I have time to make a thoughtful decision, I see intuition as a hindrance.
maxdancona

1
Thu 14 Feb, 2013 02:12 pm
@maxdancona,
I will also point out this thread as an example of my point. Your intuition about the number zero got in the way of you understanding the logic involved in this problem. Your intuition led you to the wrong answer (mathematically speaking).
0 Replies

dalehileman

0
Thu 14 Feb, 2013 03:04 pm
@maxdancona,
Quote:
The original question has be resolved,
Oh come on now Max

Quote:
so why not discuss intuition here.
Okay I'm willing

Quote:
…….this case is an example where the answer from "intuition" is mathematically wrong.
I presume you're referring to my intuition

Quote:
I am an engineer, and I play poker.
I am an erstwhile inventor and writer. My no. 2 Son visits tomorrow whereupon we have a beer-tasting-guessing in the jacuzzi. Can hardly wait

Quote:
Both of these pursuits are highly mathematical.
Yes they are, but intuition is very important to my two

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I intentionally exclude intuition from my decision making.
Could be a mistake, depending on the value of your Intuition

Quote:
Intuition is valuable in one rare case; when you don't have time for logic or reason.
It operates subliminally and of course you're not consciously aware of it

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The only advantage of intuition is that it is fast.
Yes usually, often

Quote:
It let's you make a decision, right or wrong, quickly, and intuition is correct some of the time just by random.
Indubitably

Quote:
I do use imagination (which is very different from intuition).
They work together

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……. Intuition closes your mind by making a decision before you have consciously thought it out.
Are you quite sure about that Max

Quote:
Einstein…….was against….."common sense"…... "a collection of prejudices……..
Common sense, Intuition, and reason work together

Quote:
For important decisions where I have time to make a thoughtful decision, I see intuition as a hindrance.
So Max how do you turn it off
0 Replies

IRFRANK

1
Thu 14 Feb, 2013 07:42 pm
@engineer,
0 Replies

Finn dAbuzz

2
Fri 15 Feb, 2013 02:53 pm
@maxdancona,
Do you believe that a decision made through intuition has simply invoked a random decision generator?

I will agree that intuition isn't very effective for problems much more complex than "Do I move from the safety of the trees into that clearing ahead?" or "Which person do I ask to watch my baggage while I go to the restroom?" but something is going on in the mind that helps to inform the decision beyond spinning a wheel of fortune and seeing on which decision is stops.

dalehileman

0
Fri 15 Feb, 2013 03:18 pm
@Finn dAbuzz,
Quote:
Do you believe that a decision made through intuition has simply invoked a random decision generator?
Don't think that's what Max meant but it did sound that way didn't it

Quote:
….isn't very effective for problems much more complex than "Do I move…...into that clearing ahead?"
Disagree, think it's much more profound. But don't want to start a war

Quote:
or "Which person do I ask to watch my baggage while I go to the restroom?"
Now this might require some pretty sharp judgement depending on many factors not accessible to the conscious--nonetheless as you say, come quick (forgive still another pun)

Quote:
but something is going on in the mind…..beyond spinning a wheel……...
Yes Buzz, much much more
0 Replies

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